Project Summary Dopamine neurons of the ventral tegmental area (VTA) provide essential modulatory signals to the forebrain limbic system and cortex to facilitate learning and motivational processes. Disruptions in dopamine signaling are broadly implicated in mental illness and likely contribute to a spectrum of behavioral dysfunction through distinct cortico-limbic pathways. The heterogeneity of dopamine neurons in the VTA has long been appreciated, but therapeutic strategies targeting the system are still based on a monolithic perspective. Recent advances in mapping the input/output relationships of distinct dopamine pathways have attempted to resolve the basic organization of the VTA, but have yielded little in the way of establishing how specialized subdivisions might be organized. Unraveling the basic anatomical and functional organization of the VTA is essential if precision therapeutics are to be achieved for treating specific behavioral dysfunctions. We hypothesized that the dopamine system in the VTA can be organized based on peptidergic modulation to gate information through specific output pathways. We have mapped the projections of dopamine neurons in the VTA that express distinct neuropeptide receptors and discovered a remarkable specialization of these outputs. Here we propose to establish the basic electrophysiological, anatomical, and behavioral function of these pathways using novel Cre driver mouse lines in combination with advanced techniques in viral-based circuit dissection. We will also establish novel methods for the genetic characterization of these subpopulations. Successful completion of our proposed aims will provide novel insight into the basic organization of the VTA dopamine system and establish a framework for cracking the dopamine code.